Nowadays, the organic EL device attracts attention as the lighting device replacing an incandescent lamp and a fluorescent lamp, and many studies are made on the organic EL device.
As used herein, the organic EL device means one in which an organic EL element is stacked on transparent substrates such as a glass substrate and a transparent resin film. In the organic EL element, two electrodes in which one or both the electrodes have translucency are opposed to each other, and a light emitting layer made of an organic compound is stacked between the electrodes. The organic EL device emits light by energy of recombination of an electron and a hole that are electrically excited.
That is, the organic EL device is a self-luminous device, and the organic EL device can emit the light having various wavelengths by properly selecting a material for the light emitting layer. The organic EL device is extremely thin compared with an incandescent lamp and a fluorescent lamp, and the organic EL device planarly emits the light. Therefore, there is few restrictions to an installation place.
In order to prevent moisture or oxygen (hereinafter, also referred to as water and the like) from invading in the organic EL element, the organic EL device has a sealing structure that blocks the organic EL element from an external atmosphere. However, in the case where the organic EL element has the insufficient sealing function, a non-luminous point called a dark spot is generated after a long period of use of the organic EL device.
The dark spot will be described in detail. In the case where the organic EL element has the insufficient sealing function, the water and the like invade in the sealing structure, and the organic EL element is exposed to the water and the like. At this point, when the organic EL element is used (lit), the electrode constituting the organic EL element is partially oxidized, and an insulating oxide layer is formed on the surface of the electrode. When the oxide layer is formed, a place where the oxide layer is formed is partially insulated. Therefore, the place does not emit the light during the lighting, but the non-luminous point (dark spot) is formed. In order to prevent the formation of the dark spot in the organic EL device, it is necessary to surely prevent the water and the like from invading in the organic EL element.
It is well known that the dark spot has a size invisible to naked eyes, formed at the beginning of the use, and it is well known that the dark spot grows with the dark spot formed at the beginning of the use as a nuclear.
The growth and expansion of the dark spot adversely affect durability and quality of the organic EL device. It is well known that generally the growth of the dark spot is promoted at an accelerated rate by heat generated in the organic EL element during the lighting.
That is, in order to constrain the growth of the formed dark spot, it is necessary that the heat generated in the organic EL element during the lighting be not retained in the organic EL element, but efficiently released to the outside.
Patent Document 1 discloses a technology of preventing the water invasion and heat retention during the lighting in the organic EL element.
The organic EL device of Patent Document 1 has an organic EL element having a structure in which a first electrode (electrode), an organic compound layer (light emitting layer), and a second electrode (electrode) are sequentially stacked on a substrate. In the organic EL device of Patent Document 1, an inorganic moisture-proof layer and a metallic conductive sealing member are provided on the second electrode. In the organic EL device of Patent Document 1, an insulating adhesive layer is interposed between the inorganic moisture-proof layer and the conductive sealing member. A conductive sealing material having excellent sealing performance (barrier property) and heat-transfer performance (heat-transfer property) is used as a conductive sealing member in the organic EL device of Patent Document 1.
In the organic EL device of Patent Document 1, using the excellent sealing performance and heat-transfer performance of the conductive sealing material, not only the water and the like is prevented from invading in the organic EL element, but also the heat is prevented from retaining on a surface (emission surface) that emits the light during lighting.